Use EnumSerializer for explicitly serializable enum instead of auto-generated

core/commonMain/src/kotlinx/serialization/internal/Enums.kt

@@ -7,6 +7,7 @@ package kotlinx.serialization.internal
 import kotlinx.serialization.*
 import kotlinx.serialization.descriptors.*
 import kotlinx.serialization.encoding.*
+import kotlin.jvm.Volatile
 
 /*
  * Descriptor used for explicitly serializable enums by the plugin.
@@ -49,20 +50,52 @@ internal class EnumDescriptor(
     }
 }
 
-// Used for enums that are not explicitly serializable by the plugin
+@OptIn(ExperimentalSerializationApi::class)
+@InternalSerializationApi
+internal fun <T : Enum<T>> createSimpleEnumSerializer(serialName: String, values: Array<T>): KSerializer<T> {
+    return EnumSerializer(serialName, values)
+}
+
+@OptIn(ExperimentalSerializationApi::class)
+@InternalSerializationApi
+internal fun <T : Enum<T>> createMarkedEnumSerializer(
+    serialName: String,
+    values: Array<T>,
+    names: Array<String?>,
+    annotations: Array<Array<Annotation>?>
+): KSerializer<T> {
+    val descriptor = EnumDescriptor(serialName, values.size)
+    values.forEachIndexed { i, v ->
+        val elementName = names.getOrNull(i) ?: v.name
+        descriptor.addElement(elementName)
+        annotations.getOrNull(i)?.forEach {
+            descriptor.pushAnnotation(it)
+        }
+    }
+
+    return EnumSerializer(serialName, values, descriptor)
+}
+
 @PublishedApi
 @OptIn(ExperimentalSerializationApi::class)
 internal class EnumSerializer<T : Enum<T>>(
     serialName: String,
     private val values: Array<T>
 ) : KSerializer<T> {
+    private var overriddenDescriptor: SerialDescriptor? = null
 
-    override val descriptor: SerialDescriptor = buildSerialDescriptor(serialName, SerialKind.ENUM) {
-        values.forEach {
-            val fqn = "$serialName.${it.name}"
-            val enumMemberDescriptor = buildSerialDescriptor(fqn, StructureKind.OBJECT)
-            element(it.name, enumMemberDescriptor)
-        }
+    internal constructor(serialName: String, values: Array<T>, descriptor: SerialDescriptor) : this(serialName, values) {
+        overriddenDescriptor = descriptor
+    }
+
+    override val descriptor: SerialDescriptor by lazy {
+        overriddenDescriptor ?: createUnmarkedDescriptor(serialName)
+    }
+
+    private fun createUnmarkedDescriptor(serialName: String): SerialDescriptor {
+        val d = EnumDescriptor(serialName, values.size)
+        values.forEach { d.addElement(it.name) }
+        return d
     }
 
     override fun serialize(encoder: Encoder, value: T) {

core/commonTest/src/kotlinx/serialization/CachedSerializersTest.kt

@@ -22,11 +22,36 @@ class CachedSerializersTest {
     @Serializable
     abstract class Abstract
 
+    @Serializable
+    enum class SerializableEnum {A, B}
+
+    @SerialInfo
+    annotation class MyAnnotation(val x: Int)
+
+    @Serializable
+    enum class SerializableMarkedEnum {
+        @SerialName("first")
+        @MyAnnotation(1)
+        C,
+        @MyAnnotation(2)
+        D
+    }
+
     @Test
     fun testObjectSerializersAreSame() = noJsLegacy {
         assertSame(Object.serializer(), Object.serializer())
     }
 
+    @Test
+    fun testSerializableEnumSerializersAreSame() = noJsLegacy {
+        assertSame(SerializableEnum.serializer(), SerializableEnum.serializer())
+    }
+
+    @Test
+    fun testSerializableMarkedEnumSerializersAreSame() = noJsLegacy {
+        assertSame(SerializableMarkedEnum.serializer(), SerializableMarkedEnum.serializer())
+    }
+
     @Test
     fun testSealedSerializersAreSame() = noJsLegacy {
         assertSame(SealedParent.serializer(), SealedParent.serializer())

core/commonTest/src/kotlinx/serialization/SerializersLookupEnumTest.kt

@@ -6,6 +6,7 @@ package kotlinx.serialization
 
 import kotlinx.serialization.descriptors.*
 import kotlinx.serialization.encoding.*
+import kotlinx.serialization.internal.EnumSerializer
 import kotlinx.serialization.test.*
 import kotlin.test.*
 
@@ -47,9 +48,45 @@ class SerializersLookupEnumTest {
     @Serializable
     enum class PlainEnum
 
+    @Serializable
+    enum class SerializableEnum { C, D }
+
+    @Serializable
+    enum class SerializableMarkedEnum { C, @SerialName("NotD") D }
+
     @Test
     fun testPlainEnum() {
-        assertEquals(PlainEnum.serializer(), serializer<PlainEnum>())
+        if (isJsLegacy()) {
+            assertSame(PlainEnum.serializer()::class, serializer<PlainEnum>()::class)
+        } else {
+            assertSame(PlainEnum.serializer(), serializer<PlainEnum>())
+        }
+
+        if (!isJs()) {
+            assertIs<EnumSerializer<PlainEnum>>(serializer<PlainEnum>())
+        }
+    }
+
+    @Test
+    fun testSerializableEnumSerializer() {
+        assertIs<EnumSerializer<SerializableEnum>>(SerializableEnum.serializer())
+
+        if (isJsLegacy()) {
+            assertSame(SerializableEnum.serializer()::class, serializer<SerializableEnum>()::class)
+        } else {
+            assertSame(SerializableEnum.serializer(), serializer<SerializableEnum>())
+        }
+    }
+
+    @Test
+    fun testSerializableMarkedEnumSerializer() {
+        assertIs<EnumSerializer<SerializableMarkedEnum>>(SerializableMarkedEnum.serializer())
+
+        if (isJsLegacy()) {
+            assertSame(SerializableMarkedEnum.serializer()::class, serializer<SerializableMarkedEnum>()::class)
+        } else {
+            assertSame(SerializableMarkedEnum.serializer(), serializer<SerializableMarkedEnum>())
+        }
     }
 
     @Test

formats/json-tests/commonTest/src/kotlinx/serialization/EnumSerializationTest.kt

@@ -127,7 +127,7 @@ class EnumSerializationTest : JsonTestBase() {
     fun testStructurallyEqualDescriptors() {
         val libraryGenerated = Wrapper.serializer().descriptor.getElementDescriptor(0)
         val codeGenerated = MyEnum2.serializer().descriptor
-        assertNotEquals(libraryGenerated::class, codeGenerated::class)
+        assertEquals(libraryGenerated::class, codeGenerated::class)
         libraryGenerated.assertDescriptorEqualsTo(codeGenerated)
     }
 }